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Author(s):	Holzer, Robert; Prall, Karoline; Wagner, Oliver Kai; Gobiet, Gerhard
Title:
Abstract:	One of the major fault zones in the Semmering area runs along the Auebach Valley. In this fault zone a combination of soft fault rocks and water bearing hard rocks led to extremely challenging conditions in the design and execution of the tunnel. In difficult conditions, overlapping exploratory drillings in front of tunnel drive are essential to improve the geological-hydrogeological model and to assess geotechnical risks. However, in the encountered geological-hydrogeological conditions, the well-established exploratory drilling methods reached their limits. Despite the ongoing risk analysis, a very large-scale water and ground inflow with subsequent tunnel face collapse and development of a sinkhole on the surface occurred during the tunnelling. This paper describes the causes of the incident and the development of procedures to cope with the problem. In addition to the geological-geotechnical analyses, the article also discusses the limitations of geotechnical surveillance in complex heterogeneous rock masses. Entlang des Auebachtals verläuft eines der Hauptstörungssysteme des Semmeringgebiets. Die unterschiedliche lithologische Zusammensetzung aus Störungsgestein und kompetenteren Bereichen sorgt in Verbindung mit Bergwasserführung für besondere Herausforderungen für die Planung und Bauausführung. Unter schwierigen Bedingungen ist eine kontinuierliche Vorauserkundung im Rahmen der Bauausführung zur laufenden Evaluierung möglicher geomechanischer Szenarien und zur Verfeinerung des dem tunnelbautechnischen Rahmenplan zugrundeliegenden Baugrundmodells unabdingbar. Unter den vorliegenden geologischen Rahmenbedingungen stoßen jedoch die gängigen Methoden der Bohrtechnik an ihre Grenzen. Trotz laufender Risikoanalyse kam es zu einem herausfordernden großmaßstäblichen Wasser- und Materialeinbruch im Vortrieb und zu Auswirkungen bis an die Geländeoberfläche. Der Beitrag beschreibt neben den Ursachen, die zum Eintritt des Ereignisses geführt haben, auch die Maßnahmen zur Bewältigung und diskutiert neben einer geologisch-geotechnischen Analyse werden auch die Grenzen der Beobachtungsmethode in einem heterogenen Gebirgsaufbau.
Source:	Geomechanics and Tunnelling 13 (2020), No. 5
Page/s:	509-518
Language of Publication:	English/German

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